This invention relates generally to the field of mobile refrigeration systems, and more particularly to a mobile refrigeration system with a hot gas heating cycle.
The known heat and defrost algorithms which control mobile refrigeration units use solenoid operated valves to control the hot gas flow. Slow heating to the setpoint as well as long defrost times are common using the prior art algorithms. At low ambient temperatures, trailer refrigeration units with hot gas heating heat very slowly, which leads to inefficiencies.
Briefly stated, a method and system for executing a hot gas heating cycle in a mobile refrigeration unit includes diverting a flow of hot gas by bypassing a condenser into a receiver and restricting the flow, thereby raising a discharge pressure and temperature of the unit. The discharge pressure of the unit is monitored, and the restriction is regulated when the discharge pressure reaches a predetermined pressure. A combination of small and large orifice hot gas valves is used, or optionally a hot gas stepper valve. A solenoid valve or an evaporator expansion valve is optionally used to meter refrigerant into the heat loop.
According to an embodiment of the invention, a method for executing a hot gas heating cycle in a mobile refrigeration unit includes the steps of (a) opening a hot gas stepper valve followed by closing a condenser valve between a condenser and a receiver; (b) monitoring a discharge pressure in the unit; (c) comparing the discharge pressure to a first predetermined pressure; (d) closing, after step (c), the hot gas stepper valve if the hot gas heating cycle is unfinished and the discharge pressure is less than the fist predetermined pressure; (e) opening, after step (c), the hot gas stepper valve if the discharge pressure is greater than or equal to the first predetermined pressure; and (f) opening, after step (c), the condenser valve followed by closing the hot gas stepper valve if the hot gas heating cycle is finished.
According to an embodiment of the invention, a method for executing a hot gas heating cycle in a mobile refrigeration unit includes the steps of opening a small orifice hot gas valve bypassing a condenser; monitoring a discharge pressure in the unit; comparing the discharge pressure to a first predetermined pressure; opening a large orifice hot gas valve when the discharge pressure is greater than the first predetermined pressure by a first specified amount; and closing one of the small orifice hot gas valve and the large orifice hot gas valve when the discharge pressure is less than the first predetermined pressure by a second specified amount.
According to an embodiment of the invention, a method for executing a hot gas heating cycle in a mobile refrigeration unit includes the steps of restricting a flow of hot gas bypassing a condenser into a receiver, thereby raising a discharge pressure of the unit; monitoring the discharge pressure of the unit; and controlling restriction of the flow of hot gas when the discharge pressure reaches a predetermined pressure.
According to an embodiment of the invention, a system for executing a hot gas heating cycle in a mobile refrigeration unit includes means for opening a hot gas stepper valve followed by closing a condenser valve between a condenser and a receiver; means for monitoring a discharge pressure in the unit; means for comparing the discharge pressure to a first predetermined pressure; means for closing the hot gas stepper valve if the hot gas heating cycle is unfinished and the discharge pressure is less than the fist predetermined pressure; means for opening the hot gas stepper valve if the discharge pressure is greater than or equal to the first predetermined pressure; and means for opening the condenser valve followed by closing the hot gas stepper valve if the hot gas heating cycle is finished.
According to an embodiment of the invention, a system for executing a hot gas heating cycle in a mobile refrigeration unit includes means for opening a small orifice hot gas valve bypassing a condenser; means for monitoring a discharge pressure in the unit; means for comparing the discharge pressure to a first predetermined pressure; means for opening a large orifice hot gas valve when the discharge pressure is greater than the first predetermined pressure by a first specified amount; and means for closing one of the small orifice hot gas valve and the large orifice hot gas valve when the discharge pressure is less than the first predetermined pressure by a second specified amount.
According to an embodiment of the invention, a system for executing a hot gas heating cycle in a mobile refrigeration unit includes means for restricting a flow of hot gas bypassing a condenser into a receiver, thereby raising a discharge pressure of the unit; means for monitoring a discharge pressure of the unit; and means for ceasing restriction of the flow of hot gas when the discharge pressure reaches a predetermined pressure.